Development in plants: sequence and plasticity

Development

The quoted definition describes the seed-to-senescence course used in this chapter. Development also includes embryogenesis before germination: NCERT’s Introduction explicitly starts the mature plant’s development from the zygote (page 166). Germination resumes embryo growth; it does not create the embryo.

Broadly, development is the sum of growth and differentiation (NCERT pages 166 and 174).

In plain words: growth makes a plant bigger and differentiation gives its cells jobs; development is the whole life story that the two write together, from a seed sprouting to a mature plant and, finally, its old age and death.

Sequence of developmental process in a plant cell

NCERT Figure 13.8 (page 173) shows the sequence for a single cell of a higher plant, and NCERT says the same applies to tissues and organs (page 172):

1. A meristematic cell goes through plasmatic growth; by cell division, some of its products remain meristematic cells.
2. Expansion (elongation), differentiation and maturation follow, giving a mature cell.
3. Through senescence, the mature cell finally reaches death.

Plasticity and heterophylly

• “Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity” (NCERT page 173).
• Heterophylly, the presence of differently shaped leaves on the same plant, is an example of plasticity (page 173). It comes in two kinds:
  • with the phase of life: in cotton, coriander and larkspur, the leaves of the juvenile plant differ in shape from those of the mature plant;
  • with the environment: in buttercup, the leaves produced in air differ in shape from those produced in water.

Intrinsic and extrinsic factors

Development in plants, both growth and differentiation, is under the control of two sets of factors (NCERT page 174):

NCERT adds that many extrinsic factors, such as temperature and light, control growth and development through plant growth regulators (page 178).

Solved examples

Common mistakes to avoid

Quick revision summary

• NCERT’s seed-to-senescence account describes development after germination; embryonic development precedes it. Broadly, development is the sum of growth and differentiation.
• A plant cell develops through plasmatic growth, expansion, differentiation and maturation into a mature cell, then senescence and death (NCERT Figure 13.8).
• Plasticity is the ability to form different structures in response to environment or phase of life; heterophylly is an example (cotton, coriander, larkspur; buttercup in air and water).
• Intrinsic factors: intracellular (genetic) and intercellular (plant growth regulators); extrinsic: light, temperature, water, oxygen, nutrition.

Questions students ask

What is the difference between growth and development in plants?

Growth is an irreversible permanent increase in size of an organ, its parts or a cell, while development includes all the changes an organism goes through in its life cycle, from germination of the seed to senescence (NCERT pages 167 and 172). Development is broadly the sum of growth and differentiation, so it covers changes in kind as well as in size: the expansion of a leaf is growth, a meristem cell maturing into a tracheary element is differentiation, and both are part of development (page 174). Growth is measured as a quantity, such as fresh weight, length or cell number (page 168), while development is, in NCERT’s words, a precise and highly ordered succession of events (page 166).

What are the stages of plant development?

The post-embryonic sequence discussed here runs from seed germination through the seedling, the plantlet and the mature plant to senescence and, eventually, death (NCERT pages 166 and 172). In its vegetative phase the plant forms roots, leaves and branches, and only then, as NCERT notes, does it flower and form fruits and seeds (page 166). A single cell goes through its own sequence, plasmatic growth, expansion, differentiation and maturation, then senescence and death, shown in NCERT Figure 13.8 (page 173).

Is plasticity in plants the same as phenotypic plasticity?

Plasticity in NCERT is wider than phenotypic plasticity as researchers use the term: NCERT counts different structures formed in response to the environment or to phases of life (NCERT page 173). Beyond the NCERT text, research papers call environment-induced changes of leaf form, such as air versus submerged leaves, heterophylly, a kind of phenotypic plasticity; a change with the phase of life, as between the juvenile and mature leaves of cotton, coriander and larkspur, is heteroblasty (Nakayama, Journal of Plant Research, 2024; Zotz and others, The Botanical Review, 2011). NCERT calls both heterophylly and both plasticity, so answer NCERT questions that way.

Practice questions

Try each question first, then open the answer to check your working.

1. Q1. What is plasticity in plants?

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   The ability of plants to follow different pathways in response to environment or phases of life to form different kinds of structures (NCERT page 173).

2. Q2. Name three plants in which juvenile and mature leaves differ in shape.

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   Cotton, coriander and larkspur (NCERT page 173).

3. Q3. Name two intrinsic factors that control development.

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   Intracellular (genetic) factors and intercellular factors, chemicals such as plant growth regulators (NCERT page 174).